1. Field of the Invention
The present invention provides an improved fin design and, more particularly, provides an optimized fin design in order to increase the heat transfer while reducing or minimizing any airside air pressure drop.
2. General State of the Art Mod Pertinent to Invention
Air-cooled heat exchangers are used extensively by the automotive industry. In such an exchanger, the tubes carry the coolant, refrigerant, oil or hot air to be cooled. Fins are added to the outside of the tube to increase the contact surface area between the heat exchanger tubes and the outside air flowing across them. The air has thermal conductivity and convection coefficients that are very low. Louvers can be added to the fins in order to enhance the airside thermal efficiency and can significantly increase heat transfer by reducing the thermal resistance.
Each fin cross section has at least one set of louvers having two blocks. Each louver set usually has the forward and rearward blocks symmetrical to each other about the center of the set. Each block has a breaking (first) louver 1, one or several normal (main) louvers 2 and a reversal (center or last) louver 3 and may also have a center neutral (flat) area 4 as shown in FIG. 1. Traditionally, the breaking louver and the reversal louver have a shorter width than the normal louvers, in order to give more space to increase the number of normal louvers.
Another louver design can also be used such as the one shown in FIG. 2. In this louver block the reversal louver has the same width xe2x80x98wxe2x80x99 as the normal louvers but does not have a central flat area, such as is shown in FIG. 1. Still other louver designs have both full width breaking and reversal louvers, as well as the central flat area, such as are shown in the FIG. 3.
Despite the advantages of each of these different louver designs, they all have some drawbacks. The louver block design in FIG. 2 is deficient because the two reversal louvers dramatically change the airflow direction. Air cannot follow the louver direction, resulting in dead area where the air speed is approximately zero in the central part between the two reversal louvers. As a result, there is no contact between xe2x80x9cfresh movingxe2x80x9d air and the central part between the two reversal louvers.
The louver in FIG. 1 brings in some improvement by adding central flat area, allowing air to flow along the profile of louver, hence increasing the contact between the xe2x80x9cfresh movingxe2x80x9d air and the inside of the center neutral area between the two reversal louvers. However, because both the breaking and reversal louvers have reduced louver width, their primary function of directing air in through the louvers is compromised. This is particularly true for the case where the core depth of heat exchanger is very limited to approximately 30 mm or less, which covers many of the automotive applications. In these cases, each block has only few main louvers. If air does not flow in a direction along the main louvers, after the breaking or reversal louver, then these few main louvers lose their efficiency.
A fin with louvers such as those shown in the FIG. 3 solved this issue by using full width breaking and reversal louvers, as well as central flat area. However, it creates a new problem. In fact as shown in the FIG. 3, the full width breaking and reversal louvers block the airflow direction to some extent. This design creates a much higher air-side pressure drop, which in turn reduces the overall air-side heat transfer for a given xe2x80x9cramxe2x80x9d air intake or for a given fan air flow capability.
The object of the present invention is to overcome the drawbacks inherent in the prior art because the reversal louvers will not dramatically change the airflow direction but rather permit air to follow the louver direction, thus preventing any dead area where the air speed is approximately zero in the central part between the two reversal louvers. The present invention provides a contact between fresh moving air and the central part between the two reversal louvers.
It is a further object of the invention to minimize air-side pressure drop, thereby preventing reduction in the overall air-side heat transfer for a given xe2x80x9cramxe2x80x9d air intake or for a given fan air flow capability.
The invention optimizes the fin design using breaking and reversal louvers whose lengths are substantially longer than the half-length of the main louver but at slightly lower angles to the fin face, in order to increase the heat transfer while reducing or minimizing the airside air pressure drop.